Functional characterization of cinnamate 4-hydroxylase from Helianthus annuus Linn using a fusion protein method

Systems engineering Escherichia coli for efficient production p-coumaric acid from glucose

P-coumaric acid (p-CA), a pant metabolite with antioxidant and anti-inflammatory activity, is extensively utilized in biomedicine, food, and cosmetics industry. In this study, a synthetic pathway (PAL) for p-CA was designed, integrating three enzymes (AtPAL2, AtC4H, AtATR2) into a higher l-phenylalanine-producing strain Escherichia coli PHE05. However, the lower soluble expression and activity of AtC4H in the PAL pathway was a bottleneck for increasing p-CA titers. To overcome this limitation, the soluble expression of AtC4H was enhanced through N-terminal modifications. And an optimal mutant, AtC4HL373T/G211H, which exhibited a 4.3-fold higher kcat/Km value compared to the wild type, was developed. In addition, metabolic engineering strategies were employed to increase the intracellular NADPH pool. Overexpression of ppnk in engineered E. coli PHCA20 led to a 13.9-folds, 1.3-folds, and 29.1% in NADPH content, the NADPH/NADP+ ratio and p-CA titer, respectively. These optimizations significantly enhance p-CA production, in a 5-L fermenter using fed-batch fermentation, the p-CA titer, yield and productivity of engineered strain E. coli PHCA20 were 3.09 g/L, 20.01 mg/g glucose, and 49.05 mg/L/h, respectively. The results presented here provide a novel way to efficiently produce the plant metabolites using an industrial strain.

Cloning and functional characterization of a cinnamate 4-hydroxylase gene from the hornwort Anthoceros angustus

Hornworts, as the sister group to liverworts and mosses, comprise bryophytes, which are critical in understanding the evolution of key land plant traits. Cinnamate 4-hydroxylase (C4H) catalyzes the second step of the phenylpropanoid pathway to synthesize the precursor of numerous phenolic compounds, such as lignin and flavonoids. However, C4H in the hornwort Anthoceros angustus has not yet been cloned and functionally characterized. In this work, we screened the transcriptome database of A. angustus and identified one C4H gene, AnanC4H. AnanC4H maintained conserved cytochrome P450 domains with other typical plant C4Hs. Ultraviolet B irradiation and exogenous application of methyl jasmonate (MeJA) induced the expression of AnanC4H to varying degrees. The coding sequence of AnanC4H was expressed in yeast, and the recombinant proteins were isolated. The recombinant proteins of AnanC4H catalyzed the conversion of trans-cinnamic acid to p-coumaric acid and catalyzed the conversion of 3-hydroxycinnamic acid to caffeic acid. AnanC4H showed higher affinity for trans-cinnamic acid than for 3-hydroxycinnamic acid, but there was no significant difference in the catalytic efficiency of AnanC4H for the two substrates in vitro. Moreover, the expression of AnanC4H in Arabidopsis thaliana led to an increase in both the lignin content and the number of lignified cells in stems. However, there was no significant change in flavonoid content in transgenic Arabidopsis plants.

MYB Transcription Factor OsC1PLSr Involves the Regulation of Purple Leaf Sheath in Rice

Although several regulators associated with purple traits in rice have been identified, the genetic basis of the purple sheath remains unclear. In the present study, F2-1 and F2-2 populations were constructed using purple sheath (H93S) and green sheath (R1173 and YHSM), respectively. In order to identify QTL loci in purple sheaths, BSA analyses were performed on the two F2 populations. A crucial QTL for purple sheath was identified, tentatively named qPLSr6, and was located in the 4.61 Mb to 6.03 Mb region of chromosome 6. Combined with expression pattern analysis of candidate genes, LOC_Os06g10350 (OsC1PLSr) was suggested as a candidate gene. The homozygous mutant KO-1 and KO-2 created through CRISPR/Cas9 editing, lost their purple leaf sheath. The RT-PCR revealed that OsC1PLSr, anthocyanin synthase (ANS), diflavonol-4-reductase (DFR), flavanone-3-hydroxylase (F3H), and flavanone-3′-hydroxylase (F3′H) expression levels were dramatically down-regulated in the mutants. The yeast report system indicated that the 145–272 aa region at the C-terminal of OsC1PLSr is a positive transcriptional activation domain. The results indicated that OsC1PLSr synthesized anthocyanins by regulating the expression of ANS, DFR, F3H, and F3′H. This study provides new insights into the genetic basis of the purple sheath.

Hrip1 mediates rice cell wall fortification and phytoalexins elicitation to confer immunity against Magnaporthe oryzae

Magnaporthe oryzae is a potent fungus that adversely affects rice yield. Combinatorial techniques of prevention, toxic chemicals, and fungicide are used to remedy rice blast infection. We reported the role of Hrip1 in cell death elicitation and expression of systematic acquired resistance that could potentially stifle M. oryzae infection. In this study, transcriptome and metabolomic techniques were used to investigate the mechanism by which Hrip1 reprogramed the transcriptome of rice seedlings to confer immunity against M. oryzae. Our results showed that Hrip1 induces cell wall thickening and phytoalexin elicitation to confer immunity against M. oryzae infection. Hrip1 activates key lignin biosynthetic genes and myeloblastosis transcription factors that act as molecular switches for lignin production. Lignin content was increased by 68.46% and more after 48 h onwards in Hrip1-treated seedlings compared to the control treatment. Further analysis of cell wall morphology using the transmission electron microscopy technique revealed over 100% cell wall robustness. Hrip1 also induced the expression of 24 diterpene synthases. These include class I and II terpene synthases, cytochrome P450 subfamilies (OsCYP76M and OsCYP71Z), and momilactones synthases. The relationship between the expression of these genes and metabolic elicitation was analyzed using ultra-performance liquid chromatography-tandem mass spectrometry. Enhanced amounts of momilactones A and B, oryzalactone, and phytocassane A and G were detected in the Hrip1-treated leaves. We also identified seven benzoxazinoid genes (BX1-BX7) that could improve rice immunity. Our findings show that Hrip1 confers dual immunity by leveraging lignin and phytoalexins for physical and chemical resistance. This study provides novel insights into the mechanisms underlying Hrip1-treated plant immunity.

A Rehmannia glutinosa cinnamate 4-hydroxylase promotes phenolic accumulation and enhances tolerance to oxidative stress

RgC4H promotes phenolic accumulation in R. glutinosa, activating the molecular networks of its antioxidant systems, and enhancing the tolerance to oxidative stresses exposed to drought, salinity and H₂O₂ conditions. Rehmannia glutinosa is of great economic importance in China and increasing R. glutinosa productivity relies, in part, on understanding its tolerance to oxidative stress. Oxidative stress is a key influencing factor for crop productivity in plants exposed to harsh conditions. In the defense mechanisms of plants against stress, phenolics serve an important antioxidant function. Cinnamate 4-hydroxylase (C4H) is the first hydroxylase in the plant phenolics biosynthesis pathway, and elucidating the molecular characteristics of this gene in R. glutinosa is essential for understanding the effect of tolerance to oxidative stress tolerance on improving yield. Using in vitro and in silico methods, a C4H gene, RgC4H, from R. glutinosa was isolated and characterized. RgC4H has 86.34-93.89% amino acid sequence identity with the equivalent protein in other plants and localized to the endoplasmic reticulum. An association between the RgC4H expression and total phenolics content observed in non-transgenic and transgenic R. glutinosa plants suggests that this gene is involved in the process of phenolics biosynthesis. Furthermore, the tolerance of R. glutinosa to drought, salinity and H₂O₂ stresses was positively or negatively altered in plants with the overexpression or knockdown of RgC4H, respectively, as indicated by the analysis in some antioxidant physiological and molecular indices. Our study highlights the important role of RgC4H in the phenolics/phenylpropanoid pathway and reveals the involvement of phenolic-mediated regulation in oxidative stress tolerance in R. glutinosa.